Operation of an internal combustion engine develops combustion byproduct gases. Combustion of a hydrocarbon fuel in air containing oxygen generally produces heat, water vapor, carbon dioxide, various carbon compounds (carbon monoxide for example) and nitrogen. A portion of these gaseous byproducts, also called “blow-by gases”, may escape from the combustion chamber into the oil sump of the engine. Such blow-by gases, which typically also include oil mist or oil vapor may be returned to the engine air intake tract, sometimes through a crankcase ventilation valve (PCV valve) and piping connecting the vapor space above the engine oil sump into the air intake tract of the engine.
Releasing such blow-by gases to the environment is to be avoided as blow-by gases contain significant quantities of hydrocarbons as well as oil mist or oil vapors and are a significant source of air pollution.
However, returning water vapors and oil mist or oil vapors into the air intake tract is also problematic. As the heated combustion blow-by gases cool, liquid vapors in the blow-by gases may condense within the engine air intake tract duct. Also entrained oil mists may accumulate on the walls of the air intake tract.
Particularly problematic is when the accumulated liquids find their way in the air intake tract into the air filter element where they may contaminate, obstruct or saturate the air filter element, resulting in increased pressure drop across the air filter and critically reducing combustion air flow to the engine.
In some cases oils and liquids carried by blow-by gases may deposit onto the throttle valve and/or the mass air flow sensor (MAF). Oily deposits on the throttle valve may capture or entrain dust and dirt in the intake air that may result in sticking or erratic operation of the throttle valve. Oily deposits on the MAF sensor may contaminate the MAF sensor, for example a heated air flow sensing wire, thereby impeding its ability to provide an accurate air flow signal to the engine management system.
It is known to provide flexible air intake tract ducts such as blow-molded or injection molded ducts. Such flexible ducts are important as their flexibility permits the air intake duct to flex or bend as the engine moves and/or “rolls” relative to other body mounted components under the motor vehicle hood.